Piston-type accumulators, in the broadest sense of the term, are a category of hydraulic accumulators which perform the function of receiving specific volumes of a pressurized liquid (hydraulic medium) from a hydraulic system and returning these volumes to the system as required. Since the hydraulic medium is under pressure, hydraulic accumulators are treated as pressurized containers and must be designed for the maximum excess operating pressure. Allowance must be made for the acceptance standards of diverse countries in which the containers are installed. In most hydraulic systems, use is currently made of hydropneumatic (gas-impinged) accumulators with separating elements. A piston separates a fluid space as a working chamber from a gas supply space as another working chamber, thereby serving as the separating element inside the accumulator housing of the piston-type accumulator. As a rule, nitrogen is used as the operating gas. The gas-tight piston to a great extent permits decoupling of gas supply space from liquid space.
The fluid component is connected to the hydraulic circuit, so that the piston-type accumulator receives fluid when the pressure rises and the gas is compressed in the process. The compressed gas expands as the pressure drops, and forces the stored pressurized fluid back into the hydraulic circuit. It is an advantage of piston-type accumulators that they can “work” in any position, but preference is to be given to a vertical arrangement with the gas side on top so that settling of fouling particles from the fluid onto the piston seals is prevented.
The essential components of a piston-type accumulator thus are an outer cylindrical tube forming an accumulator housing, a piston with a sealing system as a separating element, and closing components on the front side which are both cover elements and at the same time also include a fluid connection and a gas connection. The accumulator is as a rule assigned two functions, that of supplying the interior pressure and that of ensuring control of the piston inside the accumulator housing.
In an effort to make production of hydraulic accumulators more efficient and cost-effective, a transition has already been made to not providing a separate cover part as the closing component fastened at least on the front end side of the cylindrical tube. Rather, the closing component is configured as an integral part with the front end of the cylindrical tube. The wall of this tube is shaped in a reshaping area. WO 98/55258 discloses an appropriate example of the production of a hydraulic accumulator in the form of a diaphragm accumulator. Shaping of the closing component is effected by conventional means as a function of the type of material of the cylindrical tube by cold or hot working, for example, after flame or induction heating has been completed, by rolling or compressing. The end of the cylindrical tube is reshaped to a bottom with a collar turned outward on which a connection for the appropriate operating medium is formed. While the expenditure of production effort required for production of a diaphragm accumulator is simplified, problems arise if such processes are to be carried out for production of piston-type accumulators.